1. Field of the Invention
The present invention relates to an optical device provided with a thin resin film having a micro-asperity pattern, a manufacturing method, and an apparatus of the optical device.
2. Description of the Related Art
Nowadays, liquid crystal display devices are increasingly applied to personal computers, TV receivers, word processors, video equipment, etc. To increase the functionality and reduce the size, power consumption, cost, etc. of such electronic equipment, reflection-type liquid crystal display devices are being developed that display an image by reflecting external light instead of using a backlight.
FIG. 15 shows an example of such reflection-type liquid crystal display devices. A reflection plate 1 is disposed under a counter substrate 28 that is composed of a transparent electrode facing a liquid crystal layer 27, a color filter layer formed over the transparent electrode, and a surface glass substrate disposed over the color filter layer. The reflection plate 1 is used to increase the viewing angle of image display of the liquid crystal display device by diffuse-reflecting light coming from the counter substrate 28.
For example, reflection plates used in such reflection-type liquid crystal display devices are formed by the following melting method. A photosensitive resin material is applied, by spin coating or the like, to the surface of a glass or resin substrate or the surface of a structure in which TFT transistors, liquid crystal driving elements, etc. are formed on such a substrate. The photosensitive resin layer is processed by photolithography so as to have asperities that are generally rectangular in cross-section, and then it is subjected to a heat treatment, whereby a smooth surface is formed by surface tension etc.
A roll embossment method is also known. In this method, a melted resin is applied to the surface of a micro-asperity pattern stamper that is provided on the outer circumferential surface of an embossment roll. As the resin sheet formed with an asperity pattern is cooled and set and also pealed off the stamper surface, it is contact-bonded to the surface.
Incidentally, a method for manufacturing an ideal micro-asperity pattern is required to satisfy the following and other conditions: 1) various three-dimensional shapes can be formed and arranged regularly or randomly; 2) a surface shape is not made obtuse by heating and the processing accuracy is high; 3) a thin film having a uniform planar shape can be formed; 4) a wide selection range of resin materials is available; 5) the cycle time is short and the mass-productivity is high.
The melting method can easily form a thin film because a resin is formed on a substrate by spin coating. However, since the melting method makes use of the phenomenon that a surface shape of a resin layer is made obtuse by a heat treatment, it cannot realize acute angles nor long planar shapes. It can realize only a narrow variety of three-dimensional shapes.
The melting method has additional problems. Since the melting conditions depend on the asperity shape that is formed by photolithography, the shape dispersion tends to be large and the processing accuracy is low. A number of manufacturing steps are needed and hence the cycle time is long. The degree of freedom of selection of photosensitive materials is low.
In the roll embossment method, since the resin application step and the transfer step can be combined into a single step, the cycle time of formation of a micro-asperity pattern is short. Since the stamper is produced in advance, a desired three-dimensional shape can be realized accurately in a stable manner. Any resin material can be used as long as it is meltable; that is, the degree of freedom of selection of resin materials is high. However, the thickness of a resin sheet is one order greater than in the melting method; it is difficult to form a thin film that is as thin as several micrometers.
In reflection-type liquid crystal display devices, no backlight is used and a reflection layer is formed on an asperity pattern layer to introduce external light to a liquid crystal layer. A reflection film having the asperity pattern layer is disposed under color filters enclosed by a block matrix, and liquid crystal driving elements are disposed between the reflection film and the color filter layer or under the reflection film.
If a registration error occurs between the color filter layer and the asperity pattern, light that should enter one of R, G, and B color filters may enter a color filter adjacent to it or a sufficient quantity of light may not enter color filters because of interruption by the black matrix, as a result of which a moire may occur and lower the legibility. If a registration error occurs between the color filter layer and the liquid crystal driving elements, intended liquid crystal portions cannot be driven and hence an intended image cannot be formed.
To avoid the above problems, the reflection film having the asperity pattern is provided with asperity pattern layer alignment marks and the liquid crystal driving elements are disposed by using those alignment marks as references. On the other hand, the color filter layer is provided with filter layer alignment marks. The reflection layer and the color filter layer are registered with each other by locating the two kinds of alignment marks at the same positions.
However, conventionally, as shown in FIGS. 23A-23C, the liquid crystal driving elements 31 are disposed in two ways: under the reflection film 26 (see FIG. 23B); and over the reflection film 26 (see FIG. 23C).
In the arrangement shown in FIG. 23B, since the liquid crystal driving elements 31 are disposed under the reflection layer 26, to perform registration between the reflection layer 26 and the color filter layer 35 it is necessary to remove parts of the asperity pattern layer 4 corresponding to the alignment marks 22 and thereby enable visual or optical detection of the alignment marks 22.
In the arrangement shown in FIG. 23C in which the liquid crystal driving elements 31 and the alignment marks 22 are disposed on a transparent planarization layer 45, it is necessary to form the planarization layer 45 separately, to dispose the alignment marks 22 on the surface of the planarization layer 45 so as to correspond to respective alignment marks 4a of the asperity pattern layer 4, and dispose the liquid crystal driving elements 31 also on the surface of the planarization layer 45. This results in a problem that the number of members and manufacturing steps are large.
The present invention has been made in view of the above circumstances in the art, and an object of the invention is therefore to provide an optical device having an asperity pattern that can be formed as a thin film with high accuracy in any of various three-dimensional shapes, as well as to provide a manufacturing method and apparatus of such an optical device. In this specification, xe2x80x9cmicro-asperity patternxe2x80x9d is a generic term of asperity shapes that develop one-dimensionally or two-dimensionally and is 0.1 xcexcm to hundreds of micrometers in depth and arbitrary in width, length, and shape. Also, xe2x80x9creflection-type liquid crystal display devicexe2x80x9d is a generic term of devices in which a liquid crystal is sealed between a transparent counter substrate having a transparent electrode and an active matrix substrate having a reflection surface that is provided with a surface micro-asperity pattern.
The invention provides a manufacturing method of an optical device, comprising the steps of preparing a cylindrical die unit an outer circumferential surface of which is formed with a micro-asperity pattern; preparing a substrate that is coated with a thin resin film; holding the substrate by a transfer stage; and forming a micro-asperity pattern on the thin resin film by pressing the outer circumferential surface of the die unit against the thin resin film with pressurizing means while rolling the die unit on the thin resin film.
In this manufacturing method, a micro-asperity pattern is formed on the thin resin film that is formed on the substrate by pressing, against the thin resin film, the cylindrical die unit the outer circumferential surface of which is formed with a micro-asperity pattern. More specifically, the substrate is held by the transfer stage and the transfer stage is moved while the outer circumferential surface of the die unit is pressed against the thin resin film by the pressurizing means. A micro-asperity pattern is formed on the thin resin film as the die unit rolls on the thin resin film.
For example, as shown in FIG. 1, recesses 3a of an embossment roll 3 are pressed against the surface of a thin resin film 4. Therefore, even if air bubbles exist inside the thin resin film 4, they are pushed and moved by the recesses 3a of the embossment roll 3 in the direction opposite to the moving direction of the thin resin film 4 and are broken by projections 3b of the embossment roll 3, whereupon the air goes out of the thin resin film 4. This reduces the probability of a phenomenon that a resulting asperity pattern is deformed by air bubbles remaining in the thin resin film 4.
It is desirable that the temperature of a room is set lower than a melting temperature of the thin resin film, and that at least one of the die unit and the transfer stage be heated while control is so made that the temperature of the thin resin film is lower than its heat decomposition temperature. With this technical measure, since the modulus of elasticity of the thin resin film can be decreased and its flowability can be increased by heating it, the loads necessary for the processing such as the pressure are decreased, which makes it possible to manufacture an optical device having an accurate micro-asperity pattern.
Asperity patterns can be arranged with a desired layout by performing the operation of rolling the die unit on the thin resin film a plurality times.
It is an effective measure to adjust an angular deviation, from the rotation axis of the die unit, of a line connecting two alignment marks of the thin resin film that are located on both sides of the rotation axis of the die unit by rotating the substrate relative to the die unit in a state that the substrate is held by the transfer stage directly or indirectly.
With this technical measure, the line connecting the two alignment marks can be rotated with respect to the rotation axis of the die unit by rotating the substrate together with moving mechanisms for moving the transfer stage in the X-axis and Y-axis directions in a state that the substrate is held by the transfer stage directly.
Where the substrate is held by the transfer stage indirectly, for example, the substrate is held by the transfer stage with a substrate rotation direction adjustment mechanism 16 interposed in between (see FIG. 7), the substrate can be rotated by means of the substrate rotation direction adjustment mechanism 16. Therefore, the line connecting the two alignment marks can be rotated with respect to the rotation axis of the die unit.
This technical measure makes it possible to set the angle between the line connecting the two alignment marks and the rotation axis of the die unit at a predetermined angle such as 0xc2x0 or 90xc2x0. The substrate side and the die unit side can be registered with each other.
It is an effective measure to form a micro-asperity pattern on the thin resin film in an inert gas or a low-pressure atmosphere having a pressure that is lower than atmospheric pressure. With this technical measure, since the air is exhausted in advance from a chamber that accommodates a manufacturing apparatus of the optical device, oxygen and impurities contained in the air are also exhausted from the chamber and a micro-asperity pattern can be formed in a clean inert gas atmosphere. This prevents oxidation or change in quality of the thin resin film as well as a phenomenon that impurities stick to the thin resin film during formation of a micro-asperity pattern and are finally fixed to the micro-asperity pattern formed. This contributes to increase of the production yield of the optical device.
Particularly where the pressure inside the chamber is lowered, no air is trapped between the die unit and the thin resin film and hence a micro-asperity pattern that is free of air bubbles can be formed. During pressurization, air bubbles act as dampers and hence necessitates increase of the pressurizing force. The elimination of air bubbles allows reduction of the pressurizing force, as a result of which the residual stress of a micro-asperity pattern can be reduced. This contributes to increase of the production yield of the optical device.
The thin resin film may be made of a thermoplastic material. A thermoplastic resins becomes flowable and hence can be shaped when heated, and solidifies when cooled. A micro-asperity pattern can be formed by pressing, with a stamper, a thin resin film on the substrate that has become flowable by heating and then cooling the thin resin film by either natural cooling at room temperature or forced cooling.
The thin resin film may be made of a thermosetting resin. A thermosetting resin is set by continuing to heat it from a liquid state or a solid state. A micro-asperity pattern can be formed by coating the substrate with a liquid thin resin film and then pressing it with a stamper while heating it.
It is desirable that the die unit have a portion having an inverted shape of the shape of an intended alignment mark that will serve as a positional reference when an optical element is disposed at a prescribed position with respect to the substrate, and that the alignment mark be press-formed on the thin resin film together with a micro-asperity pattern.
With this technical measure, since the same die unit is formed with the micro-asperity pattern and the alignment mark portion, an alignment mark can be formed accurately on the thin resin film together with a micro-asperity pattern so that they have a prescribed positional relationship, whereby the position of the micro-asperity pattern can be set accurately with respect to the optical component.
The invention also provides a manufacturing apparatus of an optical device, comprising a transfer stage for holding a substrate that is coated with a thin resin film; a cylindrical die unit an outer circumferential surface of which is formed with a micro-asperity pattern; a moving mechanism for moving the transfer stage in a direction that crosses a rotation axis of the die unit; and a pressurizing mechanism for pressing the outer circumferential surface of the die unit against the thin resin film in such a manner that the die unit can rotate about the rotation axis, wherein a micro-asperity pattern is formed on the thin resin film as the die unit rolls on the thin resin film while being pressed against the thin resin film.
In this manufacturing apparatus, the die unit rolls on the thin resin film while the outer circumferential surface of the die unit is pressed against the thin resin film by the pressurizing mechanism that is provided in such a manner that the die unit can rotate about its rotation axis. Either the thin resin film or the die unit may be moved.
In this manufacturing apparatus, a micro-asperity pattern is formed by pressing the cylindrical die unit whose outer circumferential surface is formed with the micro-asperity pattern against the thin resin film formed on the substrate.
Therefore, even if air bubbles exist inside the thin resin film 4, they are pushed and moved by recesses of the asperity pattern of the die unit in the direction opposite to the moving direction of the thin resin film (if the thin resin film is moved) or in the moving direction of the die unit (if the die unit is moved) and are broken by projections of the asperity pattern of the die unit, whereupon the air goes out of the thin resin film. This reduces the probability of a phenomenon that a resulting asperity pattern is deformed by air bubbles remaining in the thin resin film.
It is desirable that the die unit comprise a stamper member for press-forming a micro-asperity pattern on the thin resin film and a roll body for holding the stamper member. This technical measure makes it possible to roll the die unit on the thin resin film.
It is an effective measure that the die unit comprises a stamper member for press-forming the micro-asperity pattern on the thin resin film, a roll body for holding the stamper member, and an elastic member interposed between the stamper member and the roll body.
With this technical measure, the elastic member absorbs manufacturing errors such as undulation, warping, and surface roughness of the substrate, the stamper member, the roll body, etc. and thereby increases the processing accuracy of a micro-asperity pattern.
It is an effective measure that the manufacturing apparatus further comprises a heating unit for heating the die unit and the transfer stage, and a temperature control section for controlling the heating unit. This technical measure uniformizes the material characteristics of the thin resin film and increases the processing accuracy.
It is desirable that the manufacturing apparatus further comprise a rotation axis direction moving mechanism for moving the transfer stage in the direction of the rotation axis of the die unit. This technical measure makes it possible to adjust the movement position of the die unit.
It is an effective measure that the manufacturing apparatus further comprises a rotary moving mechanism for rotating the substrate in a plane that is located under the die unit and is parallel with the rotation axis of the die unit.
One possible structure is such that the rotary moving mechanism is provided over the transfer stage and the substrate is held by the rotary moving mechanism. Another possible structure is such that the rotary moving mechanism is provided under the transfer stage and the substrate is held by the transfer stage. This technical measure makes it possible to adjust the micro-asperity pattern forming direction with respect to the die unit moving direction by rotating the substrate in a plane that is located under the die unit and is parallel with the rotation axis of the die unit.
It is an effective measure that the manufacturing apparatus further comprises at least one alignment mark observation optical device provided in the pressurizing mechanism, for observing at least one alignment mark formed on the substrate.
It is also an effective measure that the manufacturing apparatus further comprises at least one alignment mark observation optical device provided under the substrate, for observing at least one set of a first alignment mark formed on the substrate and a second alignment mark formed on the die unit. Where the alignment mark observation optical device is provided under the substrate, it may be disposed in the transfer stage or the rotary moving mechanism or disposed so as to bridge the transfer stage and the rotary moving mechanism.
The above two technical measures make it possible to form a micro-asperity pattern with high positional accuracy.
The invention provides another manufacturing apparatus of an optical device, comprising a transfer stage for holding a substrate that is coated with a thin resin film; a cylindrical die unit an outer circumferential surface of which is formed with a micro-asperity pattern; a pressurizing mechanism for pressing the outer circumferential surface of the die unit against the thin resin film in such a manner that the die unit can rotate about a rotation axis thereof, a moving mechanism for moving one of the transfer stage and the die unit; an airtight chamber for accommodating at least the transfer stage, the die unit, the pressurizing mechanism, and the moving mechanism; and exhausting means for exhausting a gas from the airtight chamber prior to an operation that a micro-asperity pattern is formed on the thin resin film as the die unit rolls on the thin resin film while being pressed against the thin resin film.
In this manufacturing apparatus, since the exhausting means exhausts a gas from the airtight chamber prior to a micro-asperity pattern forming operation in which the die unit rolls on the thin resin film, oxygen and impurities contained in the air are also exhausted from the airtight chamber and a micro-asperity pattern can be formed in a clean inert gas atmosphere. This prevents oxidation or change in quality of the thin resin film as well as a phenomenon that impurities stick to the thin resin film during formation of a micro-asperity pattern and are finally fixed to the micro-asperity pattern formed. This contributes to increase of the production yield of the optical device.
Particularly where the pressure inside the airtight chamber is lowered, no air is trapped between the die unit and the thin resin film and hence a micro-asperity pattern that is free of air bubbles can be formed. During pressurization, air bubbles act as dampers and hence necessitates increase of the pressurizing force. The elimination of air bubbles allows reduction of the pressurizing force, as a result of which the residual stress of a micro-asperity pattern can be reduced. This contributes to increase of the production yield of the optical device.
The invention also provides an optical device comprising a substrate; and a thin resin film formed on the substrate, a top surface of the thin resin film being formed with a micro-asperity pattern and an alignment mark that will serve as a positional reference when an optical component is disposed at a prescribed position with respect to the substrate, the micro-asperity pattern and the alignment mark being formed by rolling, on an original resin film, a cylindrical die unit an outer circumferential surface of which is formed with a micro-asperity pattern and a portion having an inverted shape of a shape of the alignment mark while pressing the die unit against the original thin resin film.
This optical device is manufactured by using the die unit that is formed with the portion having the inverted shape of the shape of an alignment mark that will serve as a positional reference when an optical component is disposed at a prescribed position with respect to the substrate. Since the same die unit is formed with the micro-asperity pattern and the alignment mark portion, an alignment mark can be formed accurately on the thin resin film together with a micro-asperity pattern so that they have a prescribed positional relationship. The optical device makes it possible to set the position of the micro-asperity pattern accurately with respect to the optical component.
It is desirable that the alignment mark have a first portion that allows observation light incident on the alignment mark to go to detecting means and a second portion that does not.
With this technical measure, a light portion of an alignment mark of the optical component and the second portion of the alignment mark of the thin resin film can easily be registered with each other by locating them adjacent to each other or laying them one on another. The second portion may be such as to change the optical path of part of the observation light incident on the second portion so that the part of the observation light does not reach the detecting means. The optical path changing means may be such that a medium boundary surface is located on the optical path of incident light so as to form a proper angle with the optical path. In this manner, the optical path of incident light can easily be changed through refraction or reflection.